In many applications, it is desirable to employ an X-ray beam that is restricted in its wavelength range. Filters that are used to restrict the wavelength range are particularly important for diffraction and fluoresence applications.
The use of heavy metal filters for producing a relatively monochromatic beam from a source is well known. Several types of source/filter combinations have been developed. For instance, the use of a zirconium filter with a molybdenum source removes most of the continuous radiation from the source and produces a relatively pure K .alpha. line which can be useful for analytical purposes. Monochromatic radiation produced in this way is widely used in X-ray diffraction studies because the resulting diffraction line spectra are not complicated by extraneous lines arising from K beta radiation.
Filtration of the continuous radiation from a source has been performed using thin strips of metal. Problems exist in using thin metal strips as filtering elements in that they are not mechanically strong and are usually required to be placed and connected to a backing or support. Very thin filter elements cannot be achieved by this method of fabrication. Such a filter is disclosed in U.S. Pat. No. 4,499,591.
Typical filters for monochromatization of radiation beams are fabricated by rolling techniques. However, some materials are difficult to roll to the required thicknesses (typically from 12 to 25 microns), requiring further fabrication methods. Also, achieving a uniform thickness is difficult using rolling techniques. Thus, there is a need for an improved method of manufacture.
The oxidation of some filter materials may present a problem with filter quality. A need exists for a composite filter which protects oxidizable filter materials necessary for certain applications.